Periodic Table of the Elements Periodic Table of the Elements By Tim Sharp, Reference Editor | January 5, 2016 11:24am ET MORE The classic Periodic Table organizes the chemical elements according to the number of protons that each has in its atomic nucleus. Credit: Karl Tate, Livescience.com contributor The Periodic Table of the Elements arranges all of the known elements in an informative array. Elements are arranged in order of increasing atomic number. Order generally coincides with increasing atomic mass. The different rows of elements are called periods. The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state), according to the Los Alamos National Laboratory . The number of electrons in a period increases as one moves down the periodic table; therefore, as the energy level of the atom increases, the number of energy sub-levels per energy level increases. Elements that lie in the same column on the periodic table (called a "group") have identical valance electron configurations and consequently behave in a similar fashion chemically. For instance, all the group 18 elements are inert gases. [ Related: How Are the Elements Grouped?

] The periodic table contains an enormous amount of important information: Atomic Number: The number of protons in an atom defines what element it is. For example, carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element. Element Symbol: The element symbol is one, two or three letters chosen to represent an element ("H" for hydrogen, "Kr" for krypton, "Uup" for Ununpentium, etc.). These symbols are used internationally. Atomic Weight: The standard atomic weight is the average mass of an element in atomic mass units ("amu"). Though individual atoms always have an integer number of atomic mass units, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element. The average number of neutrons for an element can be found by subtracting the number of protons (atomic number) from the atomic mass.

Atomic weight for elements 93-118: For naturally occurring elements, the atomic weight is calculated from averaging the weights of the natural abundances of the isotopes of that element. However, for man-made trans-uranium elements there is no "natural" abundance. The convention is to list the atomic weight of the longest-lived isotope in the periodic table. These atomic weights should be considered provisional since a new isotope with a longer half-life could be produced in the future. Within this man-made category are the superheavy elements, or those with atomic numbers above 104. The larger the atom's nucleus — which increases with the number of protons inside — the more unstable that element is, generally. As such, these outsized elements are fleeting, lasting mere milliseconds before decaying into lighter elements, according to the International Union of Pure and Applied Chemistry (IUPAC). For instance, superheavy elements 113, 115, 117 and 118 were just verified by the IPUAC in December 2015, completing the seventh row, or period, on the table. Several different labs produced the superheavy elements.

"The chemistry community is eager to see its most cherished table finally being completed down to the seventh row. IUPAC has now initiated the process of formalizing names and symbols for these elements," Jan Reedijk, president of the Inorganic Chemistry Division of IUPAC, said in an IUPAC statement . Element articles alcascience6b - 2.4 Organization of the Periodic Table 2.4 Organization of the Periodic Table elements when the elements are arranged in order of increasing atomic number . ..... Click the link for more information. discovered by Dmitri I. Mendeleev Mendeleev, Dmitri Ivanovich (mĕndəlā`əf, Rus. Periodic Table and the Elements Now we're getting to the heart and soul of the way your universe works. Elements are the building blocks of all matter. We talked about quarks in the atoms section. They are smaller than the atoms of an element, but only when they group with other quarks do they form atoms that have recognizable traits. Some quarks combine to make an oxygen (O) atom. Other quarks can combine to form a nitrogen (N) atom.

It's the atoms that are different and unique, even though they are made of the same pieces. ..... Click the link for more information. and revised by Henry G. J. Moseley Moseley, Henry Gwyn Jeffreys (mōz`lē), 1887–1915, English physicist, grad. Trinity College, Oxford, 1910. ..... Click the link for more information. . In the periodic table the elements are arranged in columns and rows according to increasing atomic number atomic number, often represented by the symbol Z, the number of protons in the nucleus of an atom , as well as the number of electrons in the neutral atom. Atoms with the same atomic number make up a chemical element . ..... Click the link for more information. (see the table entitled Periodic Table Periodic Table of the Elements (showing atomic number and atomic symbol; click on atomic symbol for more detailed information) Groups ..... Click the link for more information. ). There are 18 vertical columns, or groups, in the standard periodic table. At present, there are three versions of the periodic table, each with its own unique column headings, in wide use.

The three formats are the old International Union of Pure and Applied Chemistry (IUPAC) table, the Chemical Abstract Service (CAS) table, and the new IUPAC table. The old IUPAC system labeled columns with Roman numerals followed by either the letter A or B. Columns 1 through 7 were numbered IA through VIIA, columns 8 through 10 were labeled VIIIA, columns 11 through 17 were numbered IB through VIIB and column 18 was numbered VIII. The CAS system also used Roman numerals followed by an A or B. This method, however, labeled columns 1 and 2 as IA and IIA, columns 3 through 7 as IIIB through VIB, column 8 through 10 as VIII, columns 11 and 12 as IB and IIB and columns 13 through 18 as IIIA through VIIIA. However, in the old IUPAC system the letters A and B were designated to the left and right part of the table, while in the CAS system the letters A and B were designated to the main group elements and transition elements respectively.

(The preparer of the table arbitrarily could use either an upper-or lower-case letter A or B, adding to the confusion.) Further, the old IUPAC system was more frequently used in Europe while the CAS system was most common in America. In the new IUPAC system, columns are numbered with Arabic numerals from 1 to 18. These group numbers correspond to the number of s, p, and d orbital electrons added since the last noble gas element (in column 18). This is in keeping with current interpretations of the periodic law which holds that the elements in a group have similar configurations of the outermost electron shells of their atoms. Since most chemical properties result from outer electron interactions, this tends to explain why elements in the same group exhibit similar physical and chemical properties. Unfortunately, the system fails for the elements in the first 3 periods (or rows; see below). For example, aluminum, in the column numbered 13, has only 3 s, p, and d orbital electrons. Nevertheless, the American Chemical Society has adopted the new IUPAC system. The horizontal rows of the table are called periods.

The elements of a period are characterized by the fact that they have the same number of electron shells; the number of electrons in these shells, which equals the element's atomic number, increases from left to right within each period. In each period the lighter metals appear on the left, the heavier metals in the center, and the nonmetals on the right. Elements on the borderline between metals and nonmetals are called metalloids. Group 1 (with one valence electron) and Group 2 (with two valence electrons) are called the alkali metals alkali metals, metals found in Group 1 of the periodic table . Compared to other metals they are soft and have low melting points and densities. Alkali metals are powerful reducing agents and form univalent compounds. ..... Click the link for more information. and the alkaline-earth metals alkaline-earth metals, metals constituting Group 2 of the periodic table . Generally, they are softer than most other metals, react readily with water (especially when heated), and are powerful reducing agents, but they are exceeded in each of these properties by the ..... Click the link for more information. , respectively.

Two series of elements branch off from Group 3, which contains the transition elements transition elements or transition metals, in chemistry, group of elements characterized by the filling of an inner d electron orbital as atomic number increases. ..... Click the link for more information. , or transition metals; elements 57 to 71 are called the lanthanide series lanthanide series, a series of metallic elements, included in the rare-earth metals , in Group 3 of the periodic table . Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series. ..... Click the link for more information. , or rare earths, and elements 89 to 103 are called the actinide series actinide series, a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series. ..... Click the link for more information.

, or radioactive rare earths; a third set, the superactinide series (elements 122–153), is predicted to fall outside the main body of the table, but none of these has yet been synthesized or isolated. The nonmetals in Group 17 (with seven valence electrons) are called the halogens halogen (hăl`əjĕn) [Gr. ..... Click the link for more information. . The elements grouped in the final column (Group 18) have no valence electrons and are called the inert gases inert gas or noble gas, any of the elements in Group 18 of the periodic table . In order of increasing atomic number they are: helium , neon , argon , krypton , xenon , and radon . ..... Click the link for more information. , or noble gases, because they react chemically only with extreme difficulty.

In a relatively simple type of periodic table, each position gives the name and chemical symbol for the element assigned to that position; its atomic number; its atomic weight atomic weight, mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element , as contrasted with atomic mass , which is the mass of any individual isotope. ..... Click the link for more information. (the weighted average of the masses of its stable isotopes, based on a scale in which carbon-12 has a mass of 12); and its electron configuration, i.e., the distribution of its electrons by shells. The only exceptions are the positions of elements 103 through 118; complete information on these elements has not been compiled. Larger and more complicated periodic tables may also include the following information for each element: atomic diameter or radius; common valence numbers or oxidation states; melting point; boiling point; density; specific heat; Young's modulus; the quantum states of its valence electrons; type of crystal form; stable and radioactive isotopes; and type of magnetism exhibited by the element (paramagnetism or diamagnetism). the elements of the periodic table are denomined by its moleculare estructure.

The periodic table The periodic table of elements is one of the most important tools of chemistry. Through its ingenious organization, the table provides concise and fundamental information not only about every individual element, but also about general trends across all the elements. Mastering the vagaries of the periodic table now will save you work later. This SparkNote on the Periodic Table will begin with a discussion of the table's history and then move into a description of how to read the table and describe some general periodic trends. In the next SparkNote on the basics of atomic structure, we will also cover a number of periodic trends the comprehension of which demand some knowledge of atomic structure. To see the periodic table, click [[#|here]]. Once the window appears, roll your mouse over the elements to see their specific information. You can also access the periodic table by going into the SparkNotes reference section that resides at the top of every SparkNotes page. taken from: Terms and Definitions ​At​om - The smallest unit of matter that can exist of an element. Compound - A molecule containing two or more different atoms bound together. Element - A fundamental substance that has a unique atomic number on the periodic table.

Gas - A form of matter that has mass but no definite shape, and can be either compressed or expanded to fill an infinite volume. Isotope - A different form of an element that varies by the number of neutrons in the nucleus. Liquid - A form of matter which has mass, occupies a volume, and flows to adopt the shape of its container. Solid - A form of matter which has a definite shape and volume. A Short History of the Periodic Table ​ Lavoisier's definition and list of elements helped spur an attempt by chemists to systematize and understand the elements. In 1803, the English chemist John Dalton used the general scientific recognition that elements combined with each other according to different ratios by weight to create an atomic theory that claimed all elements were built out of variable numbers of hydrogen atoms. As a part of this theory, Dalton created a scale of atomic weight based on the hydrogen atom (the weight of hydrogen was set equal to 1). In 1869, the Russian chemist Dmitry Mendeleyev organized the elements in a table according to their atomic weights (the German chemist Julius Lothar Meyer independently struck upon the same organization in 1870).

In the sixty-seven years from Dalton's formulation of atomic weight to Mendeleyev's periodic table many scientists had tried to create a working organizational structure for the elements. Mendeleyev succeeded where others failed because he realized that there existed a number of as yet unknown elements with atomic weights between the weights of already known elements. By leaving vacancies for those elements he believed were undiscovered, he hit upon an organizational scheme that seemed to vertically group elements with similar properties. Among elements with low atomic weights, he found that similar chemical characteristics recurred every seven elements. Among heavier elements, he found that characteristics resurfaced every seventeen elements. This phenomenon in which physical and chemical characteristics of elements are periodic functions of their atomic weight is called the periodic law (and gives the periodic table its name). In 1879, Mendeleyev's periodic table received a powerful boost in general acceptance when it predicted the existence of the elements gallium, germanium, and scandium. Through time, Mendeleyev's periodic table has undergone some small changes. Many, many new elements have been added. The discovery of the inert gases raised the number of elements between similar elements to eight for the lighter elements and eighteen for the darker elements.

In a few instances, scientists have discovered that organization along atomic weights does not coincide with vertical similarities. In such instances, as in the case of tellurium (Te) and iodine (I), similarity wins out over atomic weight in determining organization. taken from: Reading the Periodic Table Once again, here is a link to view a full-size periodic table: To see the periodic table, click [[#|here]]. Once the window appears, roll your mouse over the elements to see their specific information. You can also access the periodic table by going into the SparkNotes reference section that resides at the top of every SparkNotes page. General Structure of the Periodic Table As stated last section, the periodic table organizes the elements according to general patterns of similarity. Below is a very small image of the periodic table. It is basically unreadable in terms of specific information, but it allows us to easily look at the periodic tables structure general trends. Figure %: A very small periodic table The vertical columns of the periodic table (marked by yellow stripes in the figure) are called groups. The horizontal rows are called periods. There are 18 groups and 7 periods. In discussing the periodic table from here on out we will use the terms group and period.

Down a group means moving from top to bottom; across a period means moving from left to right. Reading the Periodic Table: Carbon Figure %: Description of Carbon on the Periodic Table To describe the information contained within each individual box we will use a specific example: carbon. Element Name The purpose of the element name is obvious. However, many Periodic Tables do not include element names. For those situations you must memorize the symbols that accord to each element name. Element Symbol Each element has a specific one or two letter symbol that is used interchangeably with its name. These should be memorized. Most of the time, symbols quite clearly accord to the name of the element they represent, as C accords to carbon. Occasional, however, an element's name and symbol have little relation. For example, the symbol for mercury is Hg. Atomic Number As you move across a period the atomic number increases. Similarly, as you move down a group the atomic number increases. In this way, the atomic number represents exactly where in the periodic table an element stands.

More importantly, and the reason why the ordering of the elements according to atomic number yields elements in groups with similar chemical and physical properties, the atomic number is the same as the number of protons in the nucleus of an atom of an element, and also the same as the number of electrons surrounding the nucleus in a neutral state. Carbon, for example, has six protons and six electrons. (Protons and electrons will be discussed in more detail in the Atomic Structure SparkNote) (atomicmass) Atomic Mass Along with protons, an atom also contains neutrons in its nucleus. The atomic mass (also called atomic weight) of an element is the combined number of protons and neutrons in the nucleus. Atoms of particular elements generally have different "versions," meaning that elements have atoms with different numbers of neutrons in their nucleus. These different versions are called isotopes. The atomic weight displayed is actually the weighted average of the mass numbers of the various isotopes. The atomic weight for Carbon is 12.01 because around 99% of all carbon is the carbon-12 isotope. Simple Periodic Trends Atomic Number The Atomic number increases from the top left to the bottom right. It ascends sequentially across each period.

Atomic Weight Weight The atomic weight of the elements generally increases as you move down a group and across a period. Hydrogen, at the top left of the table, is the lightest element. The unnamed element 112 is the heaviest. There are some instances when this rule does not hold true, however. For instance, because it has a high percentage of isotopes with many neutrons, the atomic weight of tellurium (Te) is higher than that for iodine (I), even though iodine has a higher atomic number. Types of Elements Elements can be organized by group or period, but they also can be placed into three distinct groups: metals, semi-metals, and non-metals. Metals Metals are the pink section on the left side of . Metals are generally lustrous solids, often deformable (though mercury (Hg) is a liquid at room temperature). Metals are highly conducive to both heat and electricity. Nonmetals Nonmetals are the blue boxes on the upper right hand of the periodic table. More than half of the non-metals are gaseous at normal temperatures. Semimetals Semimetals are the green boxes on the periodic table.

As their transitory name and placement on the periodic table suggest, they exist in between the distinctions of metals and nonmetals. Metals and Nonmetals Most chemical compounds are formed by the interactions between metals and non- metals. Further Periodic Trends Beyond those trends described here, there are a number of further periodic trends such as atomic size, ionization energy, electron affinity, and electronegativity. We will discuss these trends in the atomic structure SparkNote, since we must have a better understanding of atomic structure before getting into their specifics. Organization of the Periodic Table Topics: Lewis Dot Structures, Ionization Energy, Electronegativity Aim: What is the relationship between ionization energy and electronegativity? Do Now: On today's handout. (Review of Lewis Dot Structures and electronegativity). Behavioral Objectives: SWR: Electronegativitity, Lewis Dot Structures, properties of transition metals and noble gases. SWBAT: Define electronegativity, define ionization energy, identify elements with high and low values of each, compare ionization energy to electronegativity and understand the basis for bonding.

Motivation: A fictional story which creates an analogy to the process of the loss and gain of electrons and ultimately bonding. The story is in a language that the students should be able to easily absorb and creates a macro level context for microscopic concepts. NYC Science Standards: S1a: Demonstrates an understanding of the structure of atoms S1f: Demonstrates an understanding of interactions of energy and matter National Science Standards: Program Standard A: Teaching practices need to be consistent with the goals and curriculum framework. Teaching standard A: Select teaching and assessment strategies that support the development of student understanding and nurture a community of science learners. Teaching Standard B: Teachers of science guide and facilitate learning. Materials: Today's handouts. Reference tables. Vocabulary: Electronegativity, ionization energy, Lewis Dot Structures. Development of Lesson: - Monitors distribute graded work and collect last night's homework. 1. Students will complete the `do now' assignment independently. (2-3 minutes). 2. Selected students will put their answers on the board. 3. Review of the `do now' answers as a class. (3-4 minutes). 4. Read the story together as a class. (6-8 minutes). 5.

Students meet in groups to answer questions about the story. (12 minutes). 6. Review answers to questions (students report out). (8 minutes). 7. Answer summarizing questions as a class. (5 minutes). Summary: Questions to be answered on today's handout. (Including aim question). Homework: Worksheet to be handed out today. Due Monday. Also, notecard assignement due Monday. Elements as Building Blocks As you probably saw, the periodic table is organized like a big grid. The elementsare placed in specific places because of the way they look and act. If you have ever looked at a grid, you know that there are rows (left to right) and columns (up and down). The periodic table has rows and columns, too, and they each mean something different. You've got Your Periods... Periodic Table showing Periods Even though they skip some squares in between, all of the rows go left to right. When you look at a periodic table, each of the rows is considered to be a different period (Get it? Like PERIODic table.). In the periodic table, elements have something in common if they are in the same row.

All of the elements in a period have the same number of atomic orbitals . Every element in the top row (the first period) has one orbital for its electrons . All of the elements in the second row (the second period) have two orbitals for their electrons. It goes down the periodic table like that. At this time, the maximum number of electron orbitals or electron shells for any element is seven. ...and Your Groups Periodic Table showing Groups Now you know about periods. The periodic table has a special name for its columns, too. When a column goes from top to bottom, it's called agroup. The elements in a group have the same number of electrons in their outer orbital. Every element in the first column (group one) has one electron in its outer shell. Every element on the second column (group two) has two electrons in the outer shell. As you keep counting the columns, you'll know how many electrons are in the outer shell. There are some exceptions to the order when you look at the transition elements , but you get the general idea. Two at the Top Periodic Table showing hydrogen and helium Hydrogen (H) and helium (He) are special elements.

Hydrogen can have the talents and electrons of two groups, one and seven. To scientists, hydrogen is sometimes missing an electron, and sometimes it has an extra. Helium is different from all of the other elements. It can only have two electrons in its outer shell. Even though it only has two, it is still grouped with elements that have eight ( inert gases ) On this introductory day, students shall access the home page of the Periodic Adventure website at proceed to the "History of the Periodic Table" page at Students should read the biographical information on Dmitri Mendeleev and his pioneering .efforts to create the first periodic table of the elements. Students may then follow the link to view Mendeleev's first periodic table found at . Students should then be directed to follow the link to the Mendeleev Creative Writing Assignment, the second lesson in this sequence. Directions for the assignment may be found at "The Periodic Table" redirects here. For the book by Primo Levi , see The Periodic Table (book) . The periodic table of the chemical elements (also Mendeleev's table, periodic table of the elements or just periodic table) is a tabular display of the chemical elements .

Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior. [1 ] The periodic table is now ubiquitous within the academic discipline of chemistry , providing an extremely useful framework to classify, systematize, and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry , physics , biology , and engineering , especially chemical engineering . The current standard table contains 118 elements as of March 2010 (elements 1 – 118 ). Some versions of the table show a dark stair-step line along the metalloids. Metals are to the left of the line and non-metals to the right. [2 ] The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus ).

Rows are arranged so that elements with similar properties fall into the same columns (groups or families). According to quantum mechanical theories of electron configuration within atoms, each row (period) in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration . In printed tables, each element is usually listed with its element symbol and atomic number ; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration , electronegativity and most common valence numbers . As of 2010, the table contains 118 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been produced artificially in particle accelerators . Elements 43 (technetium), 61 (promethium) and all elements greater than 83 (bismuth), beginning with 84 (polonium) have no stable isotopes. The atomic mass of each of these element's isotope having the longest half-life is typically reported on periodic tables with parentheses.

[3 ] Isotopes of elements 43, 61, 93 (neptunium) and 94 (plutonium), first discovered synthetically, have since been discovered in trace amounts on Earth as products of natural radioactive decay processes. The primary determinant of an element's chemical properties is its electron configuration , particularly the valence shell electrons. For instance, any atoms with four valence electrons valence shell occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of electrons determines the family, or group, to which the element belongs. Subshell 7d 8p The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order (the Aufbau principle ) (see table). Hence the structure of the table. Since the outermost electrons determine chemical properties, those with the same number of valence electrons are grouped together.

Progressing through a group from lightest element to heaviest element, the outer-shell electrons (those most readily accessible for participation in chemical reactions) are all in the same type of orbital, with a similar shape, but with increasingly higher energy and average distance from the nucleus. For instance, the outer-shell (or " valence ") electrons of the first group, headed by hydrogen , all have one electron in an s orbital. In hydrogen, that s orbital is in the lowest possible energy state of any atom, the first-shell orbital (and represented by hydrogen's position in the first period of the table). In francium , the heaviest element of the group, the outer-shell electron is in the seventh-shell orbital, significantly further out on average from the nucleus than those electrons filling all the shells below it in energy. As another example, both carbon and lead have four electrons in their outer shell orbitals. Note that as atomic number (i.e., charge on the atomic nucleus ) increases, this leads to greater spin-orbit coupling between the nucleus and the electrons, reducing the validity of the quantum mechanical orbital approximation model, which considers each atomic orbital as a separate entity. The elements ununtrium , ununquadium , ununpentium , etc.

are elements that have been discovered, but so far have not received a trivial name yet. There is a system for naming them temporarily . A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the alkali metals , alkaline earth metals , halogens , pnictogens , chalcogens , and noble gases . Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers. Periods Main article: Period (periodic table) A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or " transition metals "), and especially for the f-block , where the lanthanides and actinides form two substantial horizontal series of elements.

Blocks This diagram shows the periodic table blocks .Main article: Periodic table block Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as periodic table blocks , named according to the subshell in which the "last" electron resides. The s-block comprises the first two groups ( alkali metals and alkaline earth metals ) as well as hydrogen and helium . The p-block comprises the last six groups (groups 13 through 18) and contains, among others, all of the semimetals . The d-block comprises groups 3 through 12 and contains all of the transition metals . The f-block , usually offset below the rest of the periodic table, comprises the rare earth metals . Other The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as transition metals , poor metals , and metalloids . Other informal groupings exist, such as the platinum group and the noble metals . Periodicity of chemical properties The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table.

It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows. Trends of groups Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their valence shell , which is the most important factor in accounting for their similar properties. Elements in the same group also show patterns in their atomic radius , ionization energy , and electronegativity . From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus. Trends of periods Periodic trend for ionization energy . Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases. Elements in the same period show trends in atomic radius , ionization energy , electron affinity , and electronegativity .

Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases. History Main article: History of the periodic table In 1789, Antoine Lavoisier published a list of 33 chemical elements . Although Lavoisier grouped the elements into gases , metals , non-metals , and earths , chemists spent the following century searching for a more precise classification scheme.

In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium , sodium , and potassium , for example, were grouped together as being soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third. [4 ] This became known as the Law of triads .[ citation needed ] German chemist Leopold Gmelin Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all. [4 ] worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four. Methane , for example, has one carbon atom and four hydrogen atoms.

This concept eventually became known as valency . In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency. [5 ] English chemist John Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements: When listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music . [6 ] [7 ] This law of octaves, however, was ridiculed by his contemporaries. [8 ] Portrait of Dmitri Mendeleev Russian chemistry professor Dmitri Ivanovich Mendeleev and Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively. They both constructed their tables in a similar manner: by listing the elements in a row or column in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.

[9 ] [10 ] Mendeleev was not the first chemist to do so, but he went a step further by using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium . [11 ] The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as cobalt and nickel , to better classify them into chemical families. With the development of theories of atomic structure , it became apparent that Mendeleev had inadvertently listed the elements in order of increasing atomic number . [12 ] The success of Mendeleev's table came from two decisions he made: The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered. With the development of modern quantum mechanical theories of electron configurations within atoms, it became apparent that each row (or period) in the table corresponded to the filling of a quantum shell of electrons. In Mendeleev's original table, each period was the same length. However, because larger atoms have more electron sub-shells, modern tables have progressively longer periods further down the table.

[13 ] In the years that followed after Mendeleev published his periodic table, the gaps he left were filled as chemists discovered more chemical elements. The last naturally-occurring element to be discovered was francium (referred to by Mendeleev as eka-caesium) in 1939. [14 ] The periodic table has also grown with the addition of synthetic and transuranic elements . The first transuranic element to be discovered was neptunium , which was formed by bombarding uranium with neutrons in a cyclotron in 1939. [15 What is the Periodic Table of The Elements? "It is a huge, efficient resource!" The periodic table is the most important chemistry reference there is. It arranges all the known elements in an informative array. Elements are arranged left to right and top to bottom in order of increasing atomic number . Order generally coincides with increasing atomic mass . The different rows of elements are called periods. The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state).

The number of electrons in a period increases as one traverses down the periodic table; therefore, as the energy level of the atom increases, the number of energy sub-levels per energy level increases. Using the data in the table scientists, students, and others that are familiar with the periodic table can extract information concerning individual elements. For instance, a scientist can use carbon's atomic mass to determine how many carbon atoms there are in a 1 kilogram block of carbon. People also gain information from the periodic table by looking at how it is put together. By examining an element's position on the periodic table, one can infer the electron configuration. Elements that lie in the same column on the periodic table (called a "group") have identical valance electron configurations and consequently behave in a similar fashion chemically. For instance, all the group 18 elements are inert gases. The periodic table contains an enormous amount of important information. People familiar with how the table is put together can quickly determine a significant amount of information about an element, even if they have never heard of it. taken from: The periodic table of the chemical elements (also Mendeleev's table, periodic table of the elements or just periodic table) is a tabular display of the chemical elements.

Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.[1] The periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize, and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry, physics, biology, and engineering, especially chemical engineering. The current standard table contains 118 elements as of March 2010 (elements 1–118). History of the periodic table In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, non-metals, and earths, chemists spent the following century searching for a more precise classification scheme.

In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as being soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third.[4] This became known as the Law of triads.[citation needed] German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.[4] German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency.

In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency.[5] English chemist John Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements: When listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music.[6][7] This law of octaves, however, was ridiculed by his contemporaries.[8] Portrait of Dmitri Mendeleev Russian chemistry professor Dmitri Ivanovich Mendeleev and Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively.

They both constructed their tables in a similar manner: by listing the elements in a row or column in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.[9] The success of Mendeleev's table came from two decisions he made: The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered.[10] Mendeleev was not the first chemist to do so, but he went a step further by using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium.[11] The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as cobalt and nickel, to better classify them into chemical families. With the development of theories of atomic structure, it became apparent that Mendeleev had inadvertently listed the elements in order of increasing atomic number.[12] With the development of modern quantum mechanical theories of electron configurations within atoms, it became apparent that each row (or period) in the table corresponded to the filling of a quantum shell of electrons. In Mendeleev's original table, each period was the same length.

However, because larger atoms have more electron sub-shells, modern tables have progressively longer periods further down the table.[13] In the years that followed after Mendeleev published his periodic table, the gaps he left were filled as chemists discovered more chemical elements. The last naturally-occurring element to be discovered was francium (referred to by Mendeleev as eka-caesium) in 1939.[14] The periodic table has also grown with the addition of synthetic and transuranic elements. The first transuranic element to be discovered was neptunium, which was formed by bombarding uranium with neutrons in a cyclotron in 1939.[15] plese dont touch thank you bye bye de david munera betancur In 1789, building upon the work of precursors and contemporaries alike, the French chemist Antoine Laurent Lavoisier first defined an element as a fundamental substance that could not be broken down by any chemical means then known. In the same Treatise on Chemical Elements, he compiled a list of 33 elements (a number of which were not actually elements) and devised a naming system for the discovery of new elements.

Lavoisier's definition and list of elements helped spur an attempt by chemists to systematize and understand the elements. In 1803, the English chemist John Dalton used the general scientific recognition that elements combined with each other according to different ratios by weight to create an atomic theory that claimed all elements were built out of variable numbers of hydrogen atoms. As a part of this theory, Dalton created a scale of atomic weight based on the hydrogen atom (the weight of hydrogen was set equal to 1). In 1869, the Russian chemist Dmitry Mendeleyev organized the elements in a table according to their atomic weights (the German chemist Julius Lothar Meyer independently struck upon the same organization in 1870). In the sixty-seven years from Dalton's formulation of atomic weight to Mendeleyev's periodic table many scientists had tried to create a working organizational structure for the elements. Mendeleyev succeeded where others failed because he realized that there existed a number of as yet unknown elements with atomic weights between the weights of already known elements. By leaving vacancies for those elements he believed were undiscovered, he hit upon an organizational scheme that seemed to vertically group elements with similar properties.

Among elements with low atomic weights, he found that similar chemical characteristics recurred every seven elements. Among heavier elements, he found that characteristics resurfaced every seventeen elements. This phenomenon in which physical and chemical characteristics of elements are periodic functions of their atomic weight is called the periodic law (and gives the periodic table its name). In 1879, Mendeleyev's periodic table received a powerful boost in general acceptance when it predicted the existence of the elements gallium, germanium, and scandium. Through time, Mendeleyev's periodic table has undergone some small changes. Many, many new elements have been added. The discovery of the inert gases raised the number of elements between similar elements to eight for the lighter elements and eighteen for the darker elements. In a few instances, scientists have discovered that organization along atomic weights does not coincide with vertical similarities. In such instances, as in the case of tellurium (Te) and iodine (I), similarity wins out over atomic weight in determining organization.

Question: Which element in the periodic table has atomic number 8 - it is the lowest numbered element to begin with a vowel?
Answer: OXYGEN